Just six months ago, Chelsea produced one of their finest performances under Jose Mourinho, beating Valencia in Spain to reach the Champions League semi-finals.

Valencia had not lost to an English team in 11 matches at their intimidating Mestalla stadium, a run stretching back 40 years.

They were also unbeaten at home in the Champions League that season.

That record looked set to continue when they took the lead against Chelsea with a first-half strike from Fernando Morientes.

Having drawn 1-1 in the first leg at Stamford Bridge, they were now ahead 2-1 on aggregate and seemingly on their way to the last four.

But then Mourinho threw on Joe Cole at half-time and the visitors were revitalised.

Andriy Shevchenko tapped home to level the tie on 52 minutes before Michael Essien scored the winner with extra time looming.

It was a stunning victory and kept alive Chelsea's dreams of a historic quadruple.

Grant is a decent, technical manager but Mourinho is one of the greatest managers in the game

Former Chelsea playerPat Nevin

The Blues revisit the scene of that famous win on Wednesday, but the picture has changed dramatically since the game back on 10 April.

Not only has Mourinho gone but the club appear to be lurching towards a crisis.

They lie eighth in the Premier League, they have won one of their last six games - and that was against Championship side Hull - and they have scored only six goals in those matches, including the four they put past the Tigers.

After drawing at home against Rosenborg in their opening Group B game, former Blues player Pat Nevin says Chelsea must at the very least avoid defeat in Valencia on Wednesday.

"Chelsea have made it hard for themselves by drawing against Rosenborg because that was the banker three points in that group," he told BBC Sport.

CHELSEA'S FIRST 10 GAMES

Last season

8 wins, 1 draw, 1 defeat

18 goals

This season

4 wins, 4 draws, 2 defeats

12 goals

"Technically, they could still qualify if they lose to Valencia, but it would be extremely difficult, and not getting out of the group would be an absolute disaster for Chelsea."

The task of reviving Chelsea's fortunes lies with new manager Avram Grant, who the club insist is not a stop-gap option until a bigger name becomes available.

He has had a testing start to his reign.

In the league, Chelsea followed a 2-0 defeat at Manchester United with a 0-0 draw at home to Fulham. In between, they outclassed Hull in the Carling Cup but it was hardly the sort of victory likely to appease ambitious owner Roman Abramovich.

"I watched Chelsea very closely from a tactical point of view against United," said Nevin. "Grant made all the right decisions, all the ones you would expect from a good manager.

"But one of the things that makes Mourinho one of the greatest managers in the game is he doesn't make the expected changes, he makes different ones, special ones you could say.

For the first time in a long time, Chelsea are underdogs

Former Chelsea playerPat Nevin

"I'm sure Grant is a decent, technical manager but whether that's enough if you want to be one of the best teams on the planet, I'm not so sure."

Chelsea have been hit hard by injuries to Frank Lampard, Didier Drogba and Ricardo Carvalho but Nevin says Grant must address the team's formation.

"I don't know if he felt pressured into it, but for whatever reason, Mourinho changed Chelsea's system to 4-4-2 at the start of this season," said the former midfielder.

"I think he is a 4-3-3 man, with one out-and-out striker and two supporting wide men, and I'm not so sure Chelsea have the right personnel to play 4-4-2.

"That has contributed to Chelsea's stuttering start to the season. Their unbeaten home run may still be intact but they're not scoring goals and they're not the organised team they were before."